Ultrasonic transducers are known which have been used in pulse-echo mode to locate flaws and defects in tubular goods. In the pulse-echo mode, the ultrasonic transducer emits an ultrasonic wave and then waits to receive an echo from the defect. The angle of incidence and angle of reflection relative to the surface of the defect must be approximately equal. As a result, a transmitting transducer can only receive an echo from the defect surface which is approximately normal to the direction of ultrasonic wave transmission. If the defect surface is more than about five degrees off-normal to the direction of propagation, the ultrasonic wave will be reflected but will not return a sufficiently large component to the transmitting transducer for the defect to be detected.
Ultrasonic transducers have also been used in the past in pulse-echo mode to generate ultrasonic shear waves which travel peripherally around the tubular goods being examined, and to detect echoes reflected peripherally back to the transducer. Axially oriented ultrasonic transducers have also been used to generate axial shear waves and to detect axial echoes. For some purposes, ultrasonic transducers have been oriented perpendicular to the examined surface, for instance to determine wall thickness, and have been operated in a pulse-echo mode.
Utilizing the transmitting transducer as the detecting or pick-up transducer is commonly referred to as the pulse-echo mode. Utilizing separate transmitting and receiving transducers is commonly referred to as a pitch-catch through-transmission inspection. Each transducer commonly comprises a piezoelectric element and is mounted in a block of suitable material to form a search unit. Upon receipt of a suitable voltage spike, each piezoelectric element transmits an ultrasonic signal into a material with which the search unit is in intimate acoustical contact. Conversely, upon receipt of a suitable ultrasonic signal from the material, each piezoelectric element produces a voltage signal proportional to the pressure amplitude of the ultrasonic signal incident on the element. The amplitude and shape of the voltage signal produced upon receipt of an ultrasonic signal reflected from a particular acoustic discontinuity provides information about the discontinuity.
Prior art uses of ultrasonic inspection have utilized the receiving transducer to receive sound by placing the transmitting and receiving elements Generally facing one another and measuring signal loss due to the blockage of part of the sound wave before being received by the receiving transducer.
In any automatic ultrasonic flaw detection system, a major capital cost outlay is the area of the system's electronics for the flaw detection signal processing. The number of channels of a particular system will determine the number of transducer probes from which it can process signals. In order for an automated system to operate at high speeds, a wide scanning width is needed. This can be achieved by using large area single element probes for each channel of electronics, but the decrease in resolution of these larger probes often mandates smaller probes with a decreased inspection scan width. As a result, this increases the number of channels that a system will require for a given scan width.
In the past, various patents have issued relating to ultrasonic inspection devices and techniques. For example, U.S. Pat. No. 4,305,297, issued on Dec. 15, 1981, to Ries et al. teaches ultrasonic test equipment for testing the welding seam on a thick wall. This includes transducers arranged in tandem and along the welding seam. In this invention, a tandem pair inspects in any instance two surface-near zones (inner and outer surface) as well as an interior zone. One of the transducers of the pair participates in a function test. Two pairs of transducers cover the same zone, but from different sides.
U.S. Pat. No. 4,522,064, issued on Jun. 11, 1985, to J. D. McMillan provides an ultrasonic method and apparatus for determining the depth of cracks in a pipe or conduit. This apparatus includes a transmitting transducer and a receiving transducer which are placed on the outside surface of the pipe. The transmitting transducer is energized to direct a shear wave beam of ultrasonic energy at the crack so as to generate a complex reflected wave front from the crack. This wave front contains the information as to the size of the crack in relation to the wall thickness. The receiving transducer is moved relative to the transmitting transducer until a peak or maximum amplitude reading is found.
U.S. Pat. No. 4,523,468, issued on Jun. 18, 1985, to Derkacs et al. provides a phased array inspection of cylindrical objects. A first array of ultrasonic transducers transmits ultrasonic shear waves circumferentially around an examined cylindrical object. A second array transmits ultrasonic shear waves axially along the examined object. Triggering pulses from a triggering amplifier are switched by a multiplexer to each individual transducer of the first and second arrays. As one of the transducers assumes the role of a transmitting transducer and transmits an ultrasonic wave, the other transducers of the first and second arrays assume a receiving mode to receive reflected ultrasonic components.
U.S. Pat. No. 4,641,531, issued on Feb. 10, 1987, to Reeves et al. (one of the present inventors) describes an ultrasonic inspection apparatus for locating multiple defects in eccentric wall tubing. A plurality of transducers are arranged in mated pairs, each of the pairs including a sender element for transmitting an ultrasonic shear wave and a receiver element for receiving a reflected ultrasonic wave component from the tubular goods being inspected. Each sender element is a point focus transducer having sufficiently high resolution to maintain detectability of defects in the tubular goods.
U.S. Pat. No. 5,165,280, issued on Nov. 24, 1992, to Sternberg et al. provides a device for testing oblong objects through the use of ultrasonic waves. A transmitting ultrasonic transducer generates ultrasonic waves that are acoustically irradiated into the respective object via a coupling medium. At least three ultrasonic transducers are arranged in a row next to one another along the line. The other ultrasonic transducers are receiving ultrasonic transducers. The other ultrasonic transducers are transmitting or transmitting/receiving ultrasonic transducers. The line is inclined along the longitudinal axis of the object by an angle which is between zero degrees and forty-five degrees.
U.S. Pat. No. 5,189,915, issued on Mar. 2, 1993, to Reinhart et al. shows a single mode ultrasonic inspection method and apparatus. This is adapted to utilize both pitch/catch and pulse/echo information obtained by using a single mode of wave propagation. The apparatus includes an ultrasonic signal transmitting assembly, a signal receiving assembly, a positioning mechanism, and an arrangement for recording the information received by the signal receiving assembly. The transmitting assembly includes at least one source transducer for transmitting shear mode ultrasonic search signals into the mass of the object to be inspected. The signal receiving assembly receives shear mode ultrasonic catch signals that are produced as the ultrasonic search signals encounter discontinuities in the mass of the object to be inspected. The signal receiving assembly also receives shear mode ultrasonic echo signals that are directed back to a first source transducer.
It is an object of the present invention to provide an ultrasonic detection system that can increase the effective scan width without a significant loss of resolution.
It is another object of the present invention to provide an ultrasonic detection system that effectively increases the speed and economics of inspection.
It is a further object of the present invention to provide an ultrasonic inspection system that minimizes the number of processing channels required for inspection.
It is still a further object of the present invention to provide an ultrasonic inspection system that is easy to manufacture, easy to use, relatively inexpensive, and very accurate.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.